Transistor, method of manufacturing same, etchant for use during manufacture of same, and system containing same

ABSTRACT

A transistor comprises a gate ( 110 ) comprising a gate electrode ( 111 ) and a gate dielectric ( 112 ), an electrically insulating cap ( 120, 720 ) over the gate, and a source/drain contact ( 130 ) adjacent to the gate. The electrically insulating cap prevents electrical contact between the gate and the source/drain contact. In one embodiment, the electrically insulating cap is formed in a trench ( 160, 660 ) that is self-aligned to the gate and that is created by the removal of a sacrificial cap using an aqueous solution comprising a carboxylic acid and a corrosion inhibitor.

FIELD OF THE INVENTION

The disclosed embodiments of the invention relate generally totransistors, and relate more particularly to protective etch stop layersfor transistors.

BACKGROUND OF THE INVENTION

As pitch scaling continues to increase the packing density oftransistors on computer chips, the separation between a transistor'ssource/drain contacts and its gate is rapidly decreasing. If currentpitch scaling trends continue, the creation of unwanted electricalcontact between source/drain contact and gate will quickly becomeunavoidable under existing transistor manufacturing techniques.Accordingly, there exists a need for transistor manufacturing methodsand structures capable of preventing the creation of such unwantedelectrical contact.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed embodiments will be better understood from a reading ofthe following detailed description, taken in conjunction with theaccompanying figures in the drawings in which:

FIG. 1 is a cross-sectional view of a transistor according to anembodiment of the invention;

FIG. 2 is a flowchart illustrating a method of manufacturing atransistor according to an embodiment of the invention;

FIG. 3 is a flowchart illustrating a method of forming an etch stoplayer according to an embodiment of the invention;

FIG. 4 is a cross sectional view of the transistor of FIG. 1 at aparticular point in its manufacturing process according to an embodimentof the invention;

FIG. 5 is a cross sectional view of the transistor of FIG. 1 at adifferent point in its manufacturing process according to an embodimentof the invention;

FIG. 6 is a cross sectional view of the transistor of FIG. 1 at adifferent point in its manufacturing process according to an embodimentof the invention;

FIG. 7 is a cross sectional view of the transistor of FIG. 1 at adifferent point in its manufacturing process according to an embodimentof the invention; and

FIG. 8 is a schematic of a system that includes a transistor accordingto an embodiment of the invention.

For simplicity and clarity of illustration, the drawing figuresillustrate the general manner of construction, and descriptions anddetails of well-known features and techniques may be omitted to avoidunnecessarily obscuring the discussion of the described embodiments ofthe invention. Additionally, elements in the drawing figures are notnecessarily drawn to scale. For example, the dimensions of some of theelements in the figures may be exaggerated relative to other elements tohelp improve understanding of embodiments of the present invention. Thesame reference numerals in different figures denote the same elements.

The terms “first,” “second,” “third,” “fourth,” and the like in thedescription and in the claims, if any, are used for distinguishingbetween similar elements and not necessarily for describing a particularsequential or chronological order. It is to be understood that the termsso used are interchangeable under appropriate circumstances such thatthe embodiments of the invention described herein are, for example,capable of operation in sequences other than those illustrated orotherwise described herein. Similarly, if a method is described hereinas comprising a series of steps, the order of such steps as presentedherein is not necessarily the only order in which such steps may beperformed, and certain of the stated steps may possibly be omittedand/or certain other steps not described herein may possibly be added tothe method. Furthermore, the terms “comprise,” “include,” “have,” andany variations thereof, are intended to cover a non-exclusive inclusion,such that a process, method, article, or apparatus that comprises a listof elements is not necessarily limited to those elements, but mayinclude other elements not expressly listed or inherent to such process,method, article, or apparatus.

The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,”“under,” and the like in the description and in the claims, if any, areused for descriptive purposes and not necessarily for describingpermanent relative positions. It is to be understood that the terms soused are interchangeable under appropriate circumstances such that theembodiments of the invention described herein are, for example, capableof operation in other orientations than those illustrated or otherwisedescribed herein. The term “coupled,” as used herein, is defined asdirectly or indirectly connected in an electrical or non-electricalmanner. Objects described herein as being “adjacent to” each other maybe in physical contact with each other, in close proximity to eachother, or in the same general region or area as each other, asappropriate for the context in which the phrase is used.

DETAILED DESCRIPTION OF THE DRAWINGS

In one embodiment of the invention, a transistor comprises a gatecomprising a gate electrode and a gate dielectric, an etch stop film orelectrically insulating cap over the gate, and a source/drain contactadjacent to the gate. The electrically insulating cap preventselectrical contact between the gate and the source/drain contact. In oneembodiment, the electrically insulating cap is formed in a trench thatis self-aligned to the gate and that is created by removing asacrificial cap using a wet etchant chemistry that comprises an aqueoussolution comprising a carboxylic acid and a corrosion inhibitor. Theelectrically insulating cap serves as a non-conducting etch stop layerthat protects the transistor gate during source/drain contact etch,thereby increasing the margin for source/drain contact registration andcritical dimension and preventing unwanted electrical contact (short)between source/drain contact and gate electrode.

Referring now to the figures, FIG. 1 is a cross-sectional view of atransistor 100 according to an embodiment of the invention. Asillustrated in FIG. 1, transistor 100 comprises a substrate 101 and agate 110 over substrate 101. Transistor 100 lies at least partiallywithin an interlayer dielectric 102 (which may also be referred to as“ILD0” because it is the first interlayer dielectric above substrate101). Gate 110 comprises a gate electrode 111 and a gate dielectric 112.As an example, gate electrode 111 can be a metal gate electrodecomprising copper or the like. In the illustrated embodiment gate 110further comprises a workfunction metal 113 between gate electrode 111and gate dielectric 112.

As another example, gate dielectric 112 can comprise a material having ahigh dielectric constant. (Such a material is referred to herein as a“high-k material” or the like.) Silicon dioxide, which has in the pastbeen widely used as a gate dielectric, has a dielectric constant (k) ofapproximately 3.9. A perfect vacuum has a dielectric constant definedas 1. Accordingly, any material having a dielectric constant greaterthan approximately 10 likely qualifies as, and is referred to herein as,a high-k material. As an example, the high-k material used in anembodiment of transistor 100 may be a hafnium-based, a zirconium-based,or a titanium-based dielectric material that may have a dielectricconstant of at least approximately 20. In a particular embodiment thehigh-k material is hafnium oxide having a dielectric constant of betweenapproximately 20 and approximately 40. In a different particularembodiment the high-k material is zirconium oxide having a dielectricconstant of between approximately 20 and approximately 40.

Transistor 100 further comprises an etch stop film or electricallyinsulating cap 120 over gate 110, a source/drain contact 130 adjacent togate 110, and spacers 140 adjacent to gate 110. As will be furtherdiscussed below, electrically insulating cap 120 prevents unwantedelectrical contact (also referred to as an “electrical short,” or simplya “short”) between gate 110 and source/drain contact 130. As an example,electrically insulating cap 120 can comprise silicon nitride (Si₃N₄) orthe like.

Transistor 100 still further comprises an electrically insulating layer150 over gate 110, a trench 160 in electrically insulating layer 150 andaligned to gate 110, and an electrically insulating layer 170 overelectrically insulating layer 150. As an example, one or both ofelectrically insulating layers 150 and 170 can comprise silicon dioxide,a dielectric such as is found in interlayer dielectric 102, or the like.Trench 160 is not readily visible in FIG. 1 because it is filled byelectrically insulating cap 120, but trench 160 or a similar trench willbe more clearly illustrated in a subsequent figure.

FIG. 2 is a flowchart illustrating a method 200 of manufacturing atransistor having a metal gate according to an embodiment of theinvention. In at least one embodiment, method 200 protects the metalgate during an etch that is part of the formation of a source/draincontact of the transistor. A step 210 of method 200 is to form an etchstop layer over the metal gate. As an example, the transistor can besimilar to transistor 100, first shown in FIG. 1. As another example,the etch stop layer and the metal gate can be similar to, respectively,electrically insulating cap 120 and gate 110, both of which were firstshown in FIG. 1. In one embodiment, forming the etch stop layercomprises aligning the etch stop layer to the metal gate.

A step 220 of method 200 is to form a source/drain contact adjacent tothe metal gate. Step 220 can be performed according to well knowntechniques. In one embodiment, step 220 can include forming a dielectricor gapfill layer that can be similar to electrically insulating layer170 shown in FIG. 1. As an example, the source/drain contact can besimilar to source/drain contact 130, first shown in FIG. 1. In oneembodiment, the etch stop layer/electrically insulating cap protects themetal gate by preventing the formation of an unwanted electricalconnection between the metal gate and the source/drain contact. As anexample, the etch stop layer/electrically insulating cap is: (1)impervious to the chemistry used during the source/drain contact etch,thus protecting the metal gate during such source/drain contact etch;and (2) electrically insulating such that no unwanted electricalconnection can be formed between the (electrically conducting) metalgate and the (electrically conducting) source/drain contact.Accordingly, and as alluded to earlier, the etch stop layer/electricallyinsulating cap allows a larger margin of error regarding source/draincontact registration, thus enabling the formation of larger source/draincontacts. Among other possible advantages, larger source/drain contactsare easier to make and/or exhibit less contact resistance.

FIG. 3 is a flowchart illustrating a method 300 of forming an etch stoplayer according to an embodiment of the invention. Accordingly, method300 can represent one method of performing step 210 of method 200.

A step 310 of method 300 is to form a first capping layer over the metalgate. As an example, the first capping layer can be similar to asacrificial capping layer 410, first shown in FIG. 4, which is a crosssectional view of transistor 100 at a particular point in itsmanufacturing process according to an embodiment of the invention. Inone embodiment, step 310 comprises electrolessly depositing the firstcapping layer. In that embodiment, and possibly in other embodiments,the first capping layer is selectively grown or otherwise formed overthe gate (as opposed to a blanket formation), meaning that followingsuch selective formation the first capping layer is located only (orsubstantially only) over the gate.

In the same or another embodiment, step 310 comprises forming a layercomprising cobalt or a cobalt alloy. It was mentioned above that themetal gate can comprise copper. Indeed, copper is perhaps the mostfrequently-used material for metal transistor gates. Cobalt is one ofonly a few metals that will grow selectively on copper (nickel isanother), and it is for at least that reason that cobalt or a cobaltalloy is used in at least one embodiment as a material in the firstcapping layer. In another embodiment nickel or a nickel alloy may beused as a material in the first capping layer.

As mentioned, FIG. 4 depicts transistor 100 at a point in itsmanufacturing process when sacrificial capping layer 410 is temporarilylocated over gate 110. As will be further discussed below, sacrificialcapping layer 410 is removed prior to the formation of the electricallyinsulating cap. As an example, and as suggested above, sacrificialcapping layer 410 can comprise cobalt, a cobalt alloy, nickel, a nickelalloy, or the like. Removing sacrificial capping layer 410 creates atrench in which an electrically insulating and protective etch stop capmay be formed, as will subsequently be discussed in greater detail.

A step 320 of method 300 is to form an electrically insulating film orelectrically insulating layer over the first capping layer. As anexample, the electrically insulating layer can be similar toelectrically insulating layer 150, first shown in FIG. 1. Electricallyinsulating layer 150, together with additional components of transistor100, is also illustrated in FIG. 5, which is a cross sectional view oftransistor 100 at a particular point in its manufacturing processaccording to an embodiment of the invention. In one embodiment, step 320comprises depositing a film of silicon dioxide or the like over thefirst capping layer.

A step 330 of method 300 is to expose the first capping layer byremoving a portion of the electrically insulating layer. In FIG. 5,electrically insulating layer 150 is depicted after the performance ofstep 330. In one embodiment, step 330 comprises planarizing andpolishing back electrically insulating layer 150 until the first cappinglayer is exposed, according to techniques known in the art.

A step 340 of method 300 is to remove the first capping layer in orderto form a trench aligned to the metal gate. As an example, the trenchcan be similar to trench 160, first shown in FIG. 1. As another example,the trench can be similar to a trench 660, first shown in FIG. 6, whichis a cross sectional view of transistor 100 at a particular point in itsmanufacturing process according to an embodiment of the invention. Asimplied by the foregoing, trench 660 can be similar to trench 160.

In one embodiment, step 340 comprises etching or dissolving the firstcapping layer using a wet etchant chemistry that is an aqueous solutioncomprising a carboxylic acid and a corrosion inhibitor. In oneembodiment, the wet etchant chemistry further comprises a buffer capableof adjusting or otherwise manipulating or controlling a pH of theaqueous solution. In the same or another embodiment, the wet etchantchemistry is selective to (protective of) the ILD0 material and to themetal that makes up the metal gate, including the metal gate electrodeand the workfunction metal that were introduced above, but is capable ofetching or dissolving the material that forms the first capping layer.Accordingly, in a particular embodiment the wet etchant chemistry iscapable of etching cobalt but is selective to copper and any additionalmaterials that form a part of the gate. In one embodiment, the wetetchant chemistry is applied to a wafer containing the transistor in animmersion (wet bench) or a spray tool.

In one embodiment, the carboxylic acid comprises no more thanapproximately 50 percent by weight of the aqueous solution and thecorrosion inhibitor comprises no greater than approximately 0.2 percentby weight of the aqueous solution. In the same or another embodiment,the buffer comprises no more than approximately 10 percent by weight ofthe aqueous solution.

In one embodiment, the carboxylic acid comprises an α-hydroxy acid, suchas citric acid, glycolic acid, lactic acid, malic acid, tartaric acid,or the like. In the same or another embodiment, the corrosion inhibitorcomprises benzotriazole, 1-Dodecanethiol, 2-Mercaptobenzimidazole, orthe like, and the buffer comprises hydrochloric acid (HCl), ammoniumhydroxide (NH₄OH), or the like.

A step 350 of method 300 is to fill the trench with an electricallyinsulating cap. As an example, the electrically insulating cap can besimilar to electrically insulating cap 120, first shown in FIG. 1. Asanother example, the electrically insulating cap can be similar to anelectrically insulating cap 720, first shown in FIG. 7, which is across-sectional view of transistor 100 at a particular point in itsmanufacturing process according to an embodiment of the invention. Asimplied by the foregoing, electrically insulating cap 720 can be similarto electrically insulating cap 120.

In one embodiment, step 350 or another step comprises depositing orotherwise forming a blanket etch stop layer over the metal gate and asurrounding interlayer dielectric (such as interlayer dielectric 102,first shown in FIG. 1) and then planarizing and removing a portion ofthe etch stop layer such that the electrically insulating cap remainsonly (or substantially only) in the trench, which is to say that theelectrically insulating cap remains only (or substantially only) overthe metal gate. As an example, the portion of the etch stop layer can beremoved in a chemical mechanical polish (CMP) operation in which theetch stop layer is polished down to the surface of the interlayerdielectric, at which point the electrically insulating cap fills orsubstantially fills the trench.

In FIG. 7, transistor 100 is depicted after the planarizing and removingof the etch stop layer, such that the etch stop layer is not shown inFIG. 7 beyond that portion of the etch stop layer that is in trench 660and is referred to as electrically insulating cap 720. In oneembodiment, transistor 100 may be transformed from the state depicted inFIG. 7 to the state depicted in FIG. 1 by the performance of step 220 ofmethod 200 and/or another step or series of steps.

FIG. 8 is a schematic of a system 800 that includes a transistor 831according to an embodiment of the invention. As illustrated in FIG. 8,system 800 comprises a board 810, a memory device 820 disposed on board810, and a processing device 830 disposed on board 810 and coupled tomemory device 820. Processing device 830 comprises transistor 831 thatin at least one embodiment may be similar to transistor 100, first shownin FIG. 1. Accordingly, in at least one embodiment, transistor 831comprises a gate comprising a gate electrode and a gate dielectric, anelectrically insulating cap over the gate, and a source/drain contactadjacent to the gate. The gate (including the gate electrode and thegate dielectric), the electrically insulating cap, and the source/draincontact are not explicitly shown in FIG. 8, but each of the statedcomponents, along with other components of transistor 831 notspecifically mentioned here, can be similar to corresponding componentsof transistor 100. Accordingly, for example, the electrically insulatingcap prevents unwanted electrical contact between the gate and thesource/drain contact.

Although the invention has been described with reference to specificembodiments, it will be understood by those skilled in the art thatvarious changes may be made without departing from the spirit or scopeof the invention. Accordingly, the disclosure of embodiments of theinvention is intended to be illustrative of the scope of the inventionand is not intended to be limiting. It is intended that the scope of theinvention shall be limited only to the extent required by the appendedclaims. For example, to one of ordinary skill in the art, it will bereadily apparent that the transistor and related substances, systems,and manufacturing methods discussed herein may be implemented in avariety of embodiments, and that the foregoing discussion of certain ofthese embodiments does not necessarily represent a complete descriptionof all possible embodiments.

Additionally, benefits, other advantages, and solutions to problems havebeen described with regard to specific embodiments. The benefits,advantages, solutions to problems, and any element or elements that maycause any benefit, advantage, or solution to occur or become morepronounced, however, are not to be construed as critical, required, oressential features or elements of any or all of the claims.

Moreover, embodiments and limitations disclosed herein are not dedicatedto the public under the doctrine of dedication if the embodiments and/orlimitations: (1) are not expressly claimed in the claims; and (2) are orare potentially equivalents of express elements and/or limitations inthe claims under the doctrine of equivalents.

1. A method of manufacturing a transistor having a metal gate, themethod comprising: forming an etch stop layer over the metal gate; andforming a source/drain contact adjacent to the metal gate, wherein:forming the etch stop layer comprises: aligning the etch stop layer tothe metal gate; forming a first capping layer over the metal gate;forming an electrically insulating layer over the first capping layer;exposing the first capping layer by removing a portion of theelectrically insulating layer; removing the first capping layer to forma trench aligned to the metal gate; and filling the trench with anelectrically insulating cap; and the etch stop layer prevents aformation of an electrical connection between the metal gate and thesource/drain contact.
 2. The method of claim 1 wherein: the metal gateis a copper gate; and forming the first capping layer comprises forminga layer comprising cobalt.
 3. The method of claim 2 wherein: removingthe first capping layer comprises etching the first capping layer usingan etchant that is an aqueous solution comprising a carboxylic acid anda corrosion inhibitor.
 4. The method of claim 3 wherein: the carboxylicacid is an α-hydroxy acid comprising no more than approximately 50percent of the aqueous solution; and the corrosion inhibitor comprisesno greater than approximately 0.2 percent of the aqueous solution. 5.The method of claim 1 wherein: forming the first capping layer compriseselectrolessly depositing the first capping layer.